Nanoscale tweezers can perform single-molecule ‘biopsies’

Newly-developed "nano-tweezers" created by university researchers can for the first time extract single molecules from live cells without destroying them – solving a long-standing research problem.

The research could help
scientists in building up a "human cell
atlas", providing new insights into how healthy cells function and what goes
wrong in diseased ones.

Dr Paolo Actis, from the School of Electronic and Electrical
Engineering at the University of Leeds, has been a key part of the research
programme, collaborating with senior chemistry professors at Imperial College
London on the interdisciplinary challenge.

Dr Actis has just received €4million from the European Commission
to lead a new project called SENTINEL
which will train academic and industry researchers to apply these type of "nanoelectrochemistry" techniques to
challenges from understanding the resistance of cancer to therapy, to neurodegeneration.
The project will also aim to develop the next generation of energy materials.

Carbon electrodes

The tweezers are formed from a sharp glass rod terminating
with a pair of electrodes made from a carbon-based material much like graphite.
The tip is less than 50 nanometres in diameter and is split into two electrodes, with a
10 to 20-nanometre gap between them. A nanometre is one-millionth of a millimetre.

By applying an alternating voltage, this small gap creates a powerful highly localised electrical field
that can trap and extract the small contents of cells such as DNA and
transcription factors  molecules that can change the activity of genes.

Dr Actis, pictured above, said: We are continuously expanding our knowledge
on how cells function, but many unanswered questions remain. This is especially
true for individual cells that are of the same type,
such as brain, muscle or fat cells, but have very different compositions
at the single-molecule level.

Cataloguing the diversity of seemingly identical cells can
help researchers to better understand fundamental cellular processes and design
improved models of disease, and even new patient-specific therapies.

However, traditional methods for studying these differences
typically involve bursting the cell, resulting in all of its contents getting
mixed. This results in the loss of
spatial information  how the contents were laid out in relation to each other,
and dynamic information, such as molecular changes in the cell over time.

The development of these nanoscale tweezers therefore
solves a major problem, and could help scientists in the future improve
understanding of how our bodies work.

Electrical field

The method is based on a phenomenon called
dielectrophoresis. The tweezers generate a sufficiently high electric field
enabling the trapping of certain objects such as single molecules and
particles. The ability to pick out individual molecules from a cell sets it
apart from alternative technologies.

The technique could potentially be used to carry out
experiments not currently possible. For example, nerve cells require much energy to fire messages around the body,
so they contain many mitochondria to help
them function. However, by adding or
removing mitochondria from individual nerve cells, researchers could better
understand their role, particularly in neurodegenerative diseases.

The new technique

Professor Joshua Edel, from the Department of Chemistry at
Imperial College London, who led the research programme, said: With our tweezers, we can extract the minimum number of
molecules that we need from a cell in real time,
without damaging it.

We have demonstrated that we can manipulate and extract several
different parts from different regions of the cell  including mitochondria
from the cell body, RNA from different locations in the cytoplasm and even DNA
from the nucleus.

Dr Alex Ivanov, also from Imperial, explained that nanoscale
tweezers could be a vital addition to scientists toolbox for manipulating
single cells and their parts.

Extracting individual molecules from the same cell with
unprecedented spatial resolution and over multiple points in time could provide
a deeper understanding of cellular
processes, and establish why cells from the same type can be very different to
each other, he said.

At Leeds, Dr Actis is working alongside Dr Lucy Stead from
the Faculty of Medicine and Health to use this technique to study how brain tumours resist therapy, in a project funded by the Brain
Tumour Charity.